Specific Adhesion of Carbohydrate Hydrogel Particles
in Competition with Multivalent Inhibitors Evaluated by AFM
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Abstract
Synthetic
glycooligomers have emerged as valuable analogues for
multivalent glycan structures in nature. These multivalent carbohydrates
bind to specific receptors and play a key role in biological processes.
In this work, we investigate the specific interaction between mannose
ligand presenting soft colloidal probes (SCPs) attached to an atomic
force microscope (AFM) cantilever and a Concanavalin A (ConA) receptor
surface in the presence of competing glycooligomer ligands. We studied
the SCP–ConA adhesion energy via the JKR approach and AFM pull-off
experiments in combination with optical microscopy allowing for simultaneous
determination of the contact area between SCP and ConA surface. We
varied the contact time, loading rate and loading force and measured
the resulting mannose/ConA interaction. The average adhesion energy
per mannose ligand on the probe was 5 kJ/mol, suggesting that a fraction
of mannose ligands presented on the SCP bound to the receptor surface.
Adhesion measurements via competitive binding of the SCP in the presence
of multivalent glycooligomer ligands did not indicate an influence
of their multivalency on the glycooligomer displacement from the ConA
surface. The absence of this “multivalency effect” indicates
that glycooligomers and ConA do not associate via chelate complexes
and shows that steric shielding by the glycooligomers does not slow
their displacement upon competitive binding of a ligand presenting
surface. These results highlight the high reversibility of carbohydrate–surface
interactions, which could be an essential feature of recognition processes
on the cell surface